Device for feeding a hydraulic load element mounted on a telescopic structure, by means of two jacks

ABSTRACT

A hydraulic drive telescopic boom is disclosed including two hydraulic piston-cylinder units connected between two telescopic boom sections and including fluid connections between the pistoncylinder units providing power transmission of hydraulic fluid from a pump to a load motor on the outer end of one boom section so as to substantially eliminate the need for flexible power conduits.

G United States Patent 1191 1111 3,858,396 Bourges Jan. 7, 1975 DEVICE FOR FEEDING A HYDRAULIC [56] References Cited LOAD ELEMENT MOUNTED ON A UNITED STATES PATENTS TELESCOPE STRUCTURE BY MEANS 0F 3,160,076 12/1964 Martin 91/414 TWO JACKS 3,481,251 12/1969 Shook 60/698 Inventor: Bernard Bourges, Le

Plessis-Belle-Ville, France Assignee: Societe Anonyme: Poclain, Oise,

France Filed: July 9, 1973 Appl. NO.Z 377,283

Foreign Application Priority Data Aug. 2, 1972 France 72.27878 U.S. Cl. 60/698, 91/414 Int. Cl. F01b 21/04 Field of Search 60/698; 91/411 R, 414

Primary Examiner-Paul E. Maslousky Attorney, Agent, or Firm-Mason, Fenwick & Lawrence [5 7] ABSTRACT A hydraulic drive telescopic boom is disclosed including two hydraulic piston-cylinder units connected between two telescopic boom sections and including fluid connections between the piston-cylinder units providing power transmission of hydraulic fluid from a pump to a load motor on the outer end of one boom section so as to substantially eliminate the need for flexible power conduits.

8 Claims, 2 Drawing Figures set. 121/- mm Jan. 7, 1975 Y 3,858,396

2 Sheets-Sheet 2 DEVICE FOR FEEDING A HYDRAULIC LOAD ELEMENT MOUNTED ON A TELESCOPIC STRUCTURE, BY MEANS OF TWO JACKS The present invention relates to a device for feeding a hydraulic load element mounted on a telescopic structure, by means of two jacks.

it is known, particularly in the field of public works machines, that equipment comprising hydraulic load elements are disposed at the end of telescopic structures. One example is given by clam-shell buckets which are actuated by a hydraulic jack and which are mounted at the end of a long telescopic frame or boom in order to be able to dig deeply.

Up to the present time, fluid is fed to such equipment by means of flexible conduits mounted on winding drums or by means of flexible conduits associated with pulleys. Such devices are expensive, complicated and, what is a serious drawback in the production of a telescopic assembly, bulky.

The invention intends to remedy this state of affairs and proposes to this end a new device, the adoption of which eliminates the earlier necessity of having to use flexible conduits in the telescopic zone of the structure.

To this end, the invention relates to a telescopic structure comprising two elements mounted to slide with respect to one another, whilst a drive device is coupled to these two elements in order to adjust the relative position therof. A hydraulic load element, connected selectively to a source of pressurised fluid and an exhaust reservoir, via inlet and delivery conduit connections fixed to a first of said two elements, is coupled to the second of these two elements.

This structure comprises a first fluid-actuated jack and a second fluid-actuated jack, each jack is of equal size and has a piston and associated rod so as to define small chambers of equal size on the rod side of each piston and large chambers of equal size on the opposite side of each piston. One jack has its cylinder fastened to one telescopic element and its rod fastened to the other telescopic element while the other jack is coupled to the telescopic elements in exactly the reverse manner; consequently, the jacks are in mechanical opposition, so that the piston rod of a first of these two jacks and the cylinder of the second of said two jacks are integral in translation with the first telescopic element, whilst the piston rod of the second jack and the cylinder of the first jack are integral in translation with the second telescopic element.

Two transfer conduits are arranged in the piston rod of one of the two jacks and open out, on the one hand, outside the end of the said rod, which is opposite the piston of the corresponding jack, on the other hand, one of the transfer conduits on one side, the other transfer conduit on the other side, and near said piston, respectively, in the small and large chambers of said jack.

Two connection conduits each permanently connect the end of one of the transfer conduits to one of the two connections fixed to the cylinder of the other jack, one of these connections opening into one of the chambers of said other jack, and the other connection opening into the other chamber of this other jack, so that the small and large chambers of the two jacks are connected together.

The connections of inlet and delivery conduits fixed on the first of the telescopic elements are connected by two first pipes, one to a small chamber, the other to a large chamber, via one of the members, piston rod or cylinder, of one of the jacks, which is integral with the first telescopic element. Finally, the load element is connected by two pipes, one to a small chamber, the other to a large chamber, by means of one of the members, piston rod or cylinder, of one of the jacks, or the group of the two connecting conduits, which is integral with the second telescopic element.

According to a first variant embodiment, the coupling of the jack, whose piston rod is provided with the two transfer conduits, is such that the cylinder of said jack is integral in translation with the first telescopic element. The first pipes are connected respectively to the small and large chambers of said jack, by means of two connections which open out into said chambers and which are fixed to said cylinder.

According to a second variant embodiment, the coupling of the jack, whose piston rod is provided with the two transfer conduits, is such that the cylinder of said jack is integral in translation with the first telescopic element. In addition, the piston rod of the other jack, which is also integral in translation with the first telescopic element, comprises two secondary transfer conduits, arranged in this piston rod. These secondary transfer conduits open out on the one hand to the outside of the end of said piston rod, which is opposite the piston of this other jack, on the other hand, one of said secondary transfer conduits on one side, the other secondary transfer conduit on the other side, and near the piston of said other jack, respectively in the small and large chambers of this other jack. in this case, the first two pipes are respectively connected to the small and to the large chamber of said other jack by two connections of said secondary transfer conduits fixed to the outside of the end of the rod of the piston of this other jack.

In both variant embodiments, the second pipes are connected to the small and large chambers of the jack, the cylinder of which is integral in translation with the second element, by means of two connections fixed on said cylinder.

Finally, it is advantageous if, in manner known per se, the drive device is constituted by a third jack, the maximum stroke of each of the first and second jacks being at least equal to the maximum stroke of said third jack.

The invention will be more readily understood on reading the following description with reference to the accompanying drawings in which:

FIGS. 1 and 2 are schematic views corresponding to two distinct embodiments of a structure according to the invention.

FIG. 1 shows a schematic section through a telescopic jib constituted by two sliding sections 1 and 2. A jack 3 is coupled between these two sections to permit the relative position thereof to be adjusted. In the present case, the cylinder 4 of this jack is integral with the section 2, whilst the piston rod 5 is articulated about axis 6 on section 1.

It will be noted that, in manner known per se, conduits 7 and 8 connect two conduits bored in the piston rod 5 and each respectively communicating on an op posite end with one of the respective chambers of the jack 3. An opposite end of conduits 7 and 8 is connected to a selectively operable three-way distributor valve 13. The delivery conduit 9 of a pump 10, which receives fluid through conduit 11 from reservoir 12,

also terminates at distributor 13, another conduit 14 connects said distributor 13 to said reservoir 12. A calibrated discharge valve 15 is interposed on a conduit 16 connected in shunt on the conduit 9. The three positions of the distributor 13 correspond:

the first, to the communication of conduits 8 and 9, and 7 and 14;

the second, the communication of conduits 9 and 14, and the isolation, at the level of distributor 13, of conduits 7 and 8;

the third, the communication of conduits 7 and 9, and 8 and 14.

A load element 17, constituted by a hydraulic motor, is coupled by means of a hook 18, to the section 2.

It will now be noted that two other jacks l9 and 20, which are identical, are coupled between sections 1 and 2, in mechanical opposition.

The first jack 19 includes a first cylinder 21 having a rod end from which a first piston 28 extends with the outer end of the first piston rod being pivotally connected to the telescopic section 1 about axis 25. The inner end of the first piston rod 22 is connected to a first piston 38 to define a small chamber 36 on the rod side of the piston and a large chamber 37 on the other side of the piston as clearly illustrated in FIG. 1. First cylinder 21 is pivotally connected at its head end to the second telescopic element 2 about an axis 23.

Similarly, the second jack includes a second cylinder containing a second piston 31 from which a second piston rod 22 extends outwardly from a rod end of the cylinder with the outer end of the second piston rod 22 being pivotally connected to the second telescopic element 2 about axis 24 as shown in FIG. 1. Additionally, the head end of the second cylinder 27 is pivotally connected to the first telescopic element 1 about axis 26 and the piston divides the cylinder into a small chamber 20a and a large chamber 20b.

The second piston rod 22 comprises a partially hollow rod member in that it includes a first fluid transfer conduit 29 and a second fluid transfer conduit 30, which, it will be noted, are mounted for integral translation with the section 2. Additionally, the pump 10 and the reservoir 12, along with the distributor 13, are mounted for integral movement with the telescopic section element 1.

A first connector conduit 32 is in fluid communication with the first fluid transfer conduit 29 on one end by means of a rod connection on the end of the second rod 22. The opposite end of the first connector conduit 32 is connected to a first small chamber fluid inlet and delivery connection means 49a adjacent the rod end of the first cylinder 21. Similarly, a second connector conduit 33 has one end connected to the second transfer conduit in rod 22 and has its other end connected to a first large chamber fluid inlet and delivery connection means 48a adjacent the head end of the first cylinder 21. Consequently, it will be seen that the first connector conduit 32 provides continuous fluid communication between the small chamber 36 of the first cylinder 21 and the small chamber 20a of the second cylinder 27 while the second connector conduit 32 provides continuous fluid communication between the large chamber 37 of the first cylinder and the large chamber 20b of the second cylinder 27.

Furthermore, a conventional device for feeding pressurised fluid similar to the assembly of pump 10, reservoir 12 and distributor 13, is provided for feeding the motor 17. This assembly is constituted by pump 39, which receives fluid from reservoir 12 by conduit 40, and delivers fluid in a conduit 41 connected to a distributor valve 42. The pump 39 and the distributor 42 are integral with the section 1. A conduit 43 is connected in shunt to the conduit 41 and connects this conduit 41 to the reservoir 12 with interposition of a calibrated discharge valve 44. A conduit 45 connects the distributor 42 with the reservoir 12 and a first motor delivery conduit 46 is connected on one end to a connection 46a on the distributor valve means 42 and is connected on its other end to a second large chamber fluid inlet and delivery connection means 47b adjacent the head end of the second cylinder 27 to provide fluid communication with the large chamber 20b as shown in FIG. 1. Additionally, a second motor delivery conduit 47 is connected on one end by means of a connection 47a to the distributor valve 42 and on its other end to a second small chamber fluid inlet and delivery connection means 46b to provide fluid communication with the small chamber 20a of the second cylinder 27. The distributor valve 42 is capable of selective movement to any one of three positions. Specifically, in a first position, the distributor 42 provides communication between conduit 41 and conduit 46; in a second position; conduits 41 and 45 are placed in communication to return the flow from pump 39 to the reservoir 12 while the conduits 46 and 47 are blocked by the distributor and a third position in which the conduit 41 communicates with the conduit 46 and the conduit 45 communicates with conduit 47.

A first load motor control conduit 48 extends from the first large chamber fluid inlet and delivery connection means 48a on the head end of cylinder 21 to a connection 17b on the hydraulic motor 17. Similarly, a second load motor conduit 49 extends from the first small chamber fluid inlet and delivery connection means 49a on the rod end of cylinder 21 to a second connection 17a on the motor 17 for a purpose to become apparent.

The second embodiment of the invention illustrated in FIG. 2 employs almost all of the elements previously described in connection with the first embodiment. However, the second embodiment differs from the first embodiment in that the first motor delivery conduit 46 is connected to a rod'connection 460 on the outer end of a first piston rod 50 in the first cylinder 21. A first transfer conduit 51 is provided in the rod 50 to communicate with motor delivery conduit 47 which is connected to a rod connection 47c so that the conduit 47 is placed in communication with the small chamber 36 of the cylinder 21. A second transfer conduit 50 is provided in the piston rod of the cylinder and communicates with the conduit 46 on one end via a rod connection 460 and has its other end communicating with the large chamber 37 of the cylinder 21 in FIG. 2.

The advantages drawn from the arrangements which have just been described will now be shown.

As a reminder, the aim pursued by proposing these new telescopic structures is the elimination of winding drums for flexible conduits.

It is therefore assumed that it is desired to modify the relative position of the sections 1 and 2, without any interest, in the first stage, in the feed of pressurised fluid to the motor 17 via pump 39, the distributor 42 being assumed to be in its second position. To this end, the jack 3 is fed by pump 10, the distributor 13 being placed for example in its first position, shown in FIG.

1. In the present case, the rod 5 returns into cylinder 4 and the section 2 returns into section 1. Then, the desired relative position being obtained, the distributor 13 is placed in its second position this enabling the sections 1 and 2 to be immobilised with respect to one another.

The following two questions are to be answered:

do the jacks 19 and 20 allow this adjustment, whilst distributor 42 for example would be in its second position? if it is possible, did this adjustment not have for a secondary effect to modify the position of the movable member of the motor 17 with respect to the fixed part of this motor? It will have been noticed that the return of the rod 5 into cylinder 4 caused, concomitantly, the return of the rod 28 in the cylinder 21 of the jack 19 and the exit of rod 22 from cylinder 27 of the jack 20, the three jacks being substantially parallel and their strokes being compatible, in particular the stroke of jacks l9 and 20 being at least equal and in fact substantially equal to that of jack 3. Consequently, the fluid driven out of chamber 200 by the rod 22 leaving is directed, through conduits 29 and 32, towards chamber 36, of the same section as chamber 20a. The displacements of piston rods 22 and 28 being equal in absolute value and being of opposite directions, the volume of fluid driven out of the chamber 20a compenses exactly for the make-up fluid in chamber 36. Obviously, the same applies to the volume driven out of chamber 37, which is directed towards chamber 20b.

Thus it is possible to adjust the relative position of the sections 1 and 2, by means of the jack 3, and in addition, this adjustment, which causes no transfer of fluid in the motor 17, in no wise modifies the adjustment of the position of the movable member of this motor 17.

If now, leaving the distributor 13 in its second position (adjustment of the relative position of the sections 1 and 2 unchanged), the distributor 42 is placed in its first position, which is shown in FIG. 1, the pump 39 delivers into conduit 41 and pipe 47. The fluid which penetrates into chamber 20b does not act on the piston 31, the whole being maintained in position by the jack 3. This fluid therefore escapes from chamber 20b through conduit 30. Then, through conduit 33, chamber 37 and pipe 48, it reaches connection 17b of the motor 17, which it actuates. The fluid delivered by the motor 17 returns to reservoir 12 via the successive elements: 17a, 49, 36, 32, 29, 20a, 46 and 45.

Of course, if the distributor 42 is placed in its third position, it would lead to actuating the motor 17 in opposite direction from the preceding one.

It will also be clearly understood that it is perfectly possible to effect simultaneously the adjustments of the telescoping of sections 1 and 2 and of position of the motor 17, these adjustments being in fact functionally independent, as has just been seen.

There is no need to insist on the equivalence of the means enabling pressurised fluid to be fed through pump 39 and delivery to be effected in reservoir 12, defined in FIG. 1 or FIG. 2.

Obviously, the pump 39 and reservoir 12 were to be connected to connections 46b and 47b in one case, 460 and 47c in the other case, fixed to the element of one of the jacks 19 or 20 which is fixed with respect to said reservoir 12 and pump 39. This fixed element is constituted by cylinder 27 in the structure of FIG. 1 and by the rod 28 in the structure of FIG. 2.

For the rest, it will have been clearly understood that the elimination of the winding drums for flexible conduits has been allowed by the fact that the conduits or pipes provided connect, each time, only two members mounted on the same section 1 or 2. Thus, with regard to FIG. 1

pipes 46 and 47 connect the cylinder 27 to the distributor 42, which are both fixed in translation with respect to the section 1;

conduits 32 and 33 connect the rod 22 to cylinder 21, both fixed with respect to the section 2;

pipes 48 and 49 connect cylinder 21 to the motor 17, both fixed with respect to section 2.

On this latter point, it will have been noted that it would still have been equivalent to connect pipes 48 and 49, not to cylinder 21, but to conduits 32 and 33, or further to rod 22.

The two arrangements described with regard to FIGS. 1 and 2, each have, further, an equivalent: that which is obtained by disposing the jacks l9 and 20 so as to fix the cylinders on the respective sections where the pistons of FIGS. 1 and 2 were fixed and vice versa. All the connections established in the arrangements of FIGS. 1 and 2 are furthermore retained, it being understood that the pump 39 is connected to the element cylinder or piston rod of the jacks 19 or 20 which is fixed with respect to section 1.

By way of indication only, we shall cite as applications of such telescopic structures:

the actuation of clam-shell buckets suspended at the end of telescopic beams of public works machines, both as far as the jack controlling the shells is concerned, and the motor for the angular orientation of the bucket, when there is one provided;

the control of the drive motor of a borer fixed to the end of a telescopic jib.

Of course, if a plurality of load elements are to be fed, as many assemblies with two feed and delivery jacks, similar to jacks 19 and 20, will be provided as there are load elements to be fed.

What is claimed is:

1. In a power-actuated telescopic structure including outer and inner axially adjustable telescopic elements mounted to slide relative to one another, drive means operatively coupled to said telescopic elements to effect axial adjustment of said telescopic elements rela tive to each other, a hydraulic load motor having first and second power'input-exhaust connections drivingly connected to an external end of one of said telescopic elements, pump means having a power fluid output for connection to said drive means and inflow conduit means connecting said pump means to a supply reservoir of activating fluid, the improvement comprising: a first fluid pressure actuated jack including a first cylinder having a head end and a rod end, a first piston in said cylinder and a first piston rod extending from said first piston axially outwardly from the rod end of said first cylinder, means connecting said first cylinder to said inner telescopic element, means connecting an outer external end portion of said first rod to said outer telescopic element for integral translational movement with said telescopic elements, a second fluid pressure actuated jack including a second cylinder having a head end and a rod end, a second piston and a second piston rod extending from said second piston outwardly externally of said head end of said second cylinder, means connecting said second cylinder to said outer telescopic element, means connecting said second piston rod to said inner telescopic element for translational movement with said telescopic elements, said first and second jacks being of substantially equal size and having their cylinders and pistons disposed in a substantially parallel longitudinally offset manner with respect to one another, said first piston in said first cylinder of said first jack defining a separation between a first small chamber in said first cylinder on the side of said first piston from which said first piston rod extends and a first large chamber in said first cylinder on the opposite side of said first piston, said second piston in said second cylinder separating the second cylinder into a second small chamber on the side of said second piston from which said second piston rod extends and a second large chamber on the opposite side of said piston, a selectively operable distributor valve, 21 source of pressurized fluid connected to said distributor valve, conduit means for providing fluid communication between said distributor valve means and the large chamber and small chamber of one cylinder, connector conduit means providing fluid communication between said small chambers and said large chambers respectively, said distributor valve including selectively operable valve means for enabling the supply of pressurized fluid to a desired one of said chambers of said one cylinder while concurrently venting the other chamber of said one cylinder, and conduit means for providing fluid communication between the small chamber and large chamber of one of said cylinders respectively with the first and second power input-exhaust connections of said load motor.

2. The invention of claim 1 wherein said conduit means providing fluid communication between the distributor valve and the large chamber and small chamber of one cylinder comprises a first motor delivery conduit connected to the small chamber of said second cylinder and a second motor delivery conduit connected to the large chamber of said second cylinder.

3. The invention of claim 2 wherein said drive means operatively coupled to said telescopic elements comprises a hydraulic jack including a cylinder connected to said inner adjustable telescopic element and a piston rod having an outer end connected to said outer adjustable telescopic element.

4. The invention of claim 2 wherein said means providing fluid communication between said small chambers and said large chambers includes first and second fluid transfer conduits extending internally along the length of said second piston rod each having an outer end terminating in a rod fluid connection means adjacent the outer end of said second piston rod, the inner end of said first fluid transfer conduit in said second piston rod terminating on one end in fluid communication with said second small chamber, the inner end of said second fluid transfer conduit in said second piston rod terminating on one end in fluid communication with said second large chamber, a first connector conduit extending between the fluid connection means on the outer end of said first fluid transfer conduit means and connector means on said first cylinder communicating with said first small chamber, and a second connector conduit extending between the fluid connection means on the outer end of said second fluid transfer conduit means and connector means on said first cylinder communicating with said first large chamber.

5. The invention of claim 4 wherein said conduit means providing communication between the small chamber and large chamber of one of said cylinders respectively with the first and second power inputexhaust connections of said load motor are connected to opposite ends of said first cylinder.

6. The invention of claim 1 wherein said conduit means providing fluid communication between the distributor valve and the large chamber and small chamber of one cylinder comprises a first motor delivery conduit and a second motor delivery conduit each in fluid communication with rod fluid connection means on the outer end of said first rod communicating with first and second fluid transfer conduits extending along the length of said first rod and having their inner ends in fluid communication respectively with said small chamber and said large chamber of said first cylinder.

7. The invention of claim 6 wherein said drive means operatively coupled to said telescopic elements comprises a hydraulic jack including a cylinder connected to said inner adjustable telescopic element and a piston rod having an outer end connected to said outer adjustable telescopic element.

8. The invention of claim 7 wherein said conduit means providing communication between the small chamber and large chamber of one of said cylinders respectively with the first and second power inputexhaust connections of said load motor are connected to opposite ends of said first cylinder. 

1. In a power-actuated telescopic structure including outer and inner axially adjustable telescopic elements mounted to slide relative to one another, drive means operatively coupled to said telescopic elements to effect axial adjustment of said telescopic elements relative to each other, a hydraulic load motor having first and second power input-exhaust connections drivingly connected to an external end of one of said telescopic elements, pump means having a power fluid output for connection to said drive means and inflow conduit means connecting said pump means to a supply reservoir of activating fluid, the improvement comprising: a first fluid pressure actuated jack including a first cylinder having a head end and a rod end, a first piston in said cylinder and a first piston rod extending from said first piston axially outwardly from the rod end of said first cylinder, means connecting said first cylinder to said inner telescopic element, means connecting an outer external end portion of said first rod to said outer telescopic element for integral translational movement with said telescopic elements, a second fluid pressure actuated jack including a second cylinder having a head end and a rod end, a second piston and a second piston rod extending from said second piston outwardly externally of said head end of said second cylinder, means connecting said second cylinder to said outer telescopic element, means connecting said second piston rod to said inner telescopic element for translational movement with said telescopic elements, said first and second jacks being of substantially equal size and having their cylinders and pistons disposed in a substantially parallel longitudinally offset manner with respect to one another, said first piston in said first cylinder of said first jack defining a separation between a first small chamber in said first cylinder on the side of said first piston from which said first piston rod extends and a first large chamber in said first cylinder on the opposite side of said first piston, said second piston in said second cylinder separating the second cylinder into a second small chamber on the side of said second piston from which said second piston rod extends and a second large chamber on the opposite side of said piston, a selectively operable distributor valve, a source of pressurized fluid connected to said distributor valve, conduit means for providing fluid communication between said distributor valve means and the large chamber and small chamber of one cylinder, connector conduit means providing fluid communication between said small chambers and said large chambers respectively, said distributor valve including selectively operable valve means for enabling the supply of pressurized fluid to a desired one of said chambers of said one cylinder while concurrently venting the other chamber of said one cylinder, and conduit means for providing fluid communication between the small chamber and large chamber of one of said cylinders respectively with the first and second power input-exhaust connections of said load motor.
 2. The invention of claim 1 wherein said conduit means providing fluid communication between the distributor valve and the large chamber and small chamber of one cylinder comprises a first motor delivery conduit connected to the small chamber of said second cylinder and a second motor delivery conduit connected to the large chamber of said second cylinder.
 3. The invention of claim 2 wherein said drive means operatively coupled to said telescopic elements comprises a hydraulic jack including a cylinder connected to said inner adjustable telescopic element and a piston rod having an outer end connected to said outer adjustable telescopic element.
 4. The invention of claim 2 wherein said means providing fluid communication between said small chambers and said large chambers includes first and second fluid transfer conduits extending internally along the length of said second piston rod each having an outer end terminating in a rod fluid connection means adjacent the outer end of said second piston rod, the inner end of said first fluid transfer conduit in said second piston rod terminating on one end in fluid communication with said second small chamber, the inner end of said second fluid transfer conduit in said second piston rod terminating on one end in fluid communication with said second large chamber, a first connector conduit extending between the fluid connection means on the outer end of said first fluid transfer conduit means and connector means on said first cylinder communicating with said first small chamber, and a second connector conduit extending between the fluid connection means on the outer end of said second fluid transfer conduit means and connector means on said first cylinder communicating with said first large chamber.
 5. The invention of claim 4 wherein said conduit means providing communication between the small chamber and large chamber of one of said cylinders respectively with the first and second power input-exhaust connections of said load motor are connected to opposite ends of said first cylinder.
 6. The invention of claim 1 wherein said conduit means providing fluid communication between the distributor valve and the large chamber and small chamber of one cylinder comprises a first motor delivery conduit and a second motor delivery conduit each in fluid communication with rod fluid connection means on the outer end of said first rod communicating with first and second fluid transfer conduits extending along the length of said first rod and having their inner ends in fluid communication respectively with said small chamber and said large chamber of said first cylinder.
 7. The invention of claim 6 wherein said drive means operatively coupled to said telescopic elements comprises a hydraulic jack including a cylinder connected to said inner adjustable telescopic element and a piston rod having an outer end connected to said outer adjustable telescopic element.
 8. The invention of claim 7 wherein said conduit means providing communication between the small chamber and large chamber of one of said cylinders respectively with the first and second power input-exhaust connections of said load motor are connected to opposite ends of said first cylinder. 